1. Field of the Invention
The present invention relates to a steam turbine rotor blade in which blades are connected with one another by covers formed at respective ends thereof.
2. Description of the Related Art
Recent years have seen a demand for increasing the blade length in a low-pressure last stage of a steam turbine aiming at increasing the efficiency and capacity thereof. There is a tendency of increasing severity of requirements for the cover with increasing blade length.
With increasing blade length, the amount of torsion of the blade (hereinafter referred to as profile) also increases, and an angle formed between the camber line of the profile and the circumferential direction tends to decrease accordingly.
With a decrease in this angle, an area for forming a cover canopy decreases making it difficult to provide a sufficient contact length and rigidity.
Further, with increasing blade length, the amount of deformation caused by the centrifugal force also increases and accordingly does the variation in a cover gap. As a result, there arises a tendency of increasing part having a large cover gap. If the cover gap increases, the contact length decreases and a problem of degraded vibration characteristics arises. In the worst case, the covers may be disconnected.
JP-A-2006-009801 discloses an art that provides a stepped portion radially formed at the leading edge of the blade in order to prevent moisture from staying by virtually eliminating moisture trapping pockets.